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264                                  TITANOTHERES                               CHAP, x
Hyracodonts, and it is suggested that when swimming it was
raised above the surface as with the Hippopotamus. "This
feature/' observes Professor Osborn, « with the long curved tusks,
undoubtedly used in uprooting, suggests the resemblance between
the habits of these animals and those of the hippopotami." There
were no horns in the Amynodonts. The face is shorter than in
the Hyracodonts, and the mastoid is covered as in recent Rhino-
ceroses. The canines are very strongly developed into tusks, but
the incisors show signs of disappearance. We know of the genera
Amynodon} Afetamynodon, and Cadurcotherium. AH except the
last, which is European, are American in range,
7am. 4.  Titanotheriiciae.—These Oligocene Ungulates, often
attaining to large dimensions, are nearly peculiar, so far as is at
present known, to the ISForth American Continent, and are at least
most abundant in it.1    Many generic names, such as Titanotherium,
Brontotherium, jE$rontopst Titanops, and Menodus, have been given
to them ; but a recent study of the entire material accessible for
description or already described has led Professor  Osborn to  the
opinion that there was but a  single genus, to which the name
Titanotkerium must be  applied.     Of this genus there are some
thirty well-characterised species, of which  the gradual evolution
can be  traced from the lowest strata of the White  River beds
where their remains occur.     An entire skeleton  of T. robustum
enables  us  to  understand the   osteology of  these forms and to
Bompare them with other Perissodactyles.     This  animal was more
than 13 feet long, standing some 7 feet  7  inches in height.     It
seems to have presented during life the aspect of a Rhinoceros with
aerliaps a touch of Elephant.     The skull is not unlike  that of a
Rhinoceros in general dimensions and shape; but there are a pair
>£ apparent horn cores anteriorly, which  are smaller in the more
incient forms and acquire a large size, a forward direction with a
iivergenee   of   the   two  in   the  later  forms.     A  glance at the
wcompanyiag  figures  of skulls  (Fig.  137)   of  early   and  later
Kfeaaotheres will exhibit the changes in this particular which the
fculls underwent in the lapse of time occupied by the deposition
rf these Oligoeene beds.     The nasals are short in the later, longer
n tite naoie early species, such as T. heloceras and T. coloradense.
^ zygomatic  arch projects much, and is "shelf-like" in the
fenoas, the skull thus getting an immense breadth, which,
3 of tlk® genus have been met with in the Balkans.